The invention relates to a coordinate measuring apparatus having a measuring table resistant to bending.
Coordinate measuring apparatuses of this kind have been known for some time from the state of the art. Two conventional variations for the measuring table are described below.
In a first variation, a granite block having the shape of a parallelepiped is used which is usually supported on a metal supporting frame. Although a granite block of this kind is especially well suited as a measuring table, the granite block has the special characteristic that it has a relatively large mass. This can lead to problems during transport or can limit considerably the possibilities for setting up the coordinate measuring apparatus.
A further variation comprises measuring plates made of cast iron. These measuring plates must be rigidly connected via a plurality of supporting elements to the foundation because of their inadequate bending stiffness and torsion stiffness. For this reason, a very complex adjustment of the measuring plate is needed. Furthermore, measuring plates of this kind can only be set up where a foundation is present so that the possibilities with respect to setting up are greatly limited.
It is an object of the invention to provide a coordinate measuring apparatus having an improved measuring table.
The invention is a coordinate measuring apparatus having a measuring table resistant to bending. The measuring table is configured as a ribbed-reinforced hollow body. It is also noted that the measuring table referred to herein is that component on which the workpiece to be measured is mounted.
A measuring table according to the invention has the significant advantage that it has a considerably lower mass than the known measuring tables made of granite. This simplifies transport and provides flexible possibilities with respect to the location of setup.
Compared to the known measuring plates made of cast iron, the measuring table according to a feature of the invention affords the advantage that it can be set up with considerably more flexibility because no foundation is required. Furthermore, a considerable simplification results for the setup of the measuring table because the setup and adjustment of the measuring table of the invention is considerably simplified. An elastic setup, for example, on damping elements is possible especially because of the considerably greater torsion stiffness and bending stiffness.
A coordinate measuring apparatus having a triangular ribbed component is disclosed in U.S. Pat. No. 4,763,420. Here, however, the concern is with only the subframe of the coordinate measuring apparatus. The measuring table, which is identified by reference numeral 10 in this publication, is however made, as known, from a heavy granite block in the same manner as the coordinate measuring apparatus described above so that even this coordinate measuring apparatus is subjected to the above-mentioned limitations with respect to assembly and the selection of the setup location.
In order to ensure the required stability, the measuring table region should be essentially triangularly rib reinforced. Triangular ribbed reinforcement is to be understood in the following as essentially linear ribs with the ribs being so mounted that a plurality of triangles are formed for a connection of different ribs to form geometrical figures.
The support points are those points on which the measuring table is supported and are advantageously arranged in such a manner that the ribs connect directly at the support points so that an optimal conduction of force is obtained and so that a high resistance to bending of the measuring table is achieved.
The measuring table can be configured as a welded construction. However, it is especially advantageous when the measuring table is a casting. The following materials can, for example, be used for this purpose: cast iron or mineral casting, such as polymer concrete.
The top side of the measuring table is completely closed; whereas, the lower side of the measuring table is interrupted by several holes which make possible access to the welding locations in the case of a welded construction. In the case of a casting, the holes serve as openings for the casting core.
The triangular ribbed region especially advantageously includes a rectangularly-shaped wall rib configuration which encloses the region of the triangular ribbed reinforcement. The support points are advantageously connected to the rectangularly-shaped wall rib reinforcement. In this way, an especially high stability is obtained.
An especially advantageous further improvement of the measuring table results when this table simultaneously takes over the function of the subframe so that the measuring table is then supported directly via corresponding feet on the foundation. This affords the special advantage that measuring table and supporting frame no longer have to be manufactured separately. For this case, the support points are pulled in somewhat from the outside of the measuring table because the feet (that is, the supporting blocks or even the damping elements on which the measuring table is mounted) have a defined lateral expansion and would otherwise extend laterally beyond the measuring table.
With the above-mentioned precondition that the support points are advantageously connected to the rectangularly-shaped wall rib reinforcement, the measuring table region is no longer supported in an outer region when the support points are pulled in from the outer side of the measuring table. In order to likewise support this outer region, further ribs can be provided which are perpendicular to the lateral wall rib reinforcement and support the overhanging measuring table region.
A further advantageous embodiment is provided when at least one side of the measuring table is used as a guide, that is, as a region in which the movable mechanism of the coordinate measuring apparatus can be movably guided. This feature affords the special advantage that no special component must be manufactured for the guidance region; instead, the measuring table can be manufactured all at one time. In contrast to the measuring table region, the region of the measuring table (which region is here arbitrarily designated the guide region) should be rectangularly rib reinforced; that is, the connection of the existing ribs to form geometric figures essentially only permits rectangles.
As described above, when the measuring table is simultaneously used as a subframe, the support points can be provided on the wall ribs which separate the measuring table region and the guide region from each other. This affords the special advantage that, on the one hand, the support points are connected to the lateral wall of the measuring table region and, on the other hand, the support points are also pulled in.
It is further noted with respect to the support points that each support point is part of at least one triangle which is formed of available ribs and within which triangle at least two further support points are located.
The number of support points are especially advantageous when three are selected because the measuring table is clearly determined with respect to its position.
The necessary stiffness of the measuring table can, however, be achieved only to a certain size of measuring table when there are three support points. When this size is reached, more support points must be used. Even for this case, the ribs are so arranged that each support point is a component of a triangle which is formed by available ribs and two further support points. The support points should then lie, for reasons of symmetry, at the corner locations of the triangle.